Figure 6. Dual populations of RNA drops can be stored offline and picoinjected at a later time.

(A) An emulsion was made consisting of two populations of drops, one containing RNA recovered from Raji cells, and the other from PC3 cells. The drops were collected into a syringe, incubated off chip, and then re-introduced into a microfluidic device to picoinject. The drops were then collected, thermocycled, and imaged. These drops are somewhat more polydisperse and displayed higher multiplexing rates (1%) than the drops picoinjected on the same device on which they were formed, which is most likely due to merger of some of the drops during incubation and reinjection. The ability to reinject emulsions following incubation to add reagents is critical for numerous droplet-based molecular biology assays. (B) Brightfield images of picoinjected emulsions. Scale bars  = 100 µm.